Highly filled epoxy resin compositions are widely used in casting processes, for example for car ignition coils. In view of the large number of castings, it is essential that the curing occurs rapidly but on the other hand all gaps need to be filled. Processes used up to now always require an extended curing step of several hours at temperatures above 100° C., for example U.S. Pat. No. 6,191,675.
Furthermore, it is known to use sulfonium salts as curing agents or curing accelerators in the heat-curing of cationically polymerizable organic compounds, in particular epoxy resins. For example, U.S. Pat. No. 5,013,814 describes such compositions.
Therefore, there is a need for highly filled epoxy resin compositions having good processing properties, such as sedimentation stability, viscosity (less than 2000 mPa s, T: 60° C., D: 50 s−1), impregnation behaviour of high voltage windings, gap filling behaviour, and requiring only a short curing step not exceeding 1 hour.